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AGU Research Spotlight (Apr 14-Apr 20, 2017)

2017-04-21 09:10:57

I. Science Policy

1. NSF Director Hopes for a Fair Budget

Córdova said that the geosciences "contribute immensely" to the Trump administration's expressed priorities of jobs, national security, and growing the economy.


2. Establish a Scientific Integrity Advisory Board, Says New Report

Such an advisory board could help scientific institutions and their sponsors uphold legal and ethical standards in scientific research.


3. Former NOAA Chief Scientist Warns of Threats to Science

Rick Spinrad frets about threats to science from the current administration's attitudes and budget priorities but remains hopeful that things can be turned around.


II. Ocean Sciences

1. How "Godzilla" El Ni?o Affected Tropical Fish in Low-Oxygen Zone

A warm period unexpectedly boosted some species of fish larvae off the coast of Mexico.


III. Hazards & Disasters

1. What Led to the Largest Volcanic Eruption in Human History?

A mineral-dating project at the Toba caldera in Indonesia sheds light on the science of supereruptions.


IV. Climate Change

1. A New Data Set to Keep a Sharper Eye on Land-Air Exchanges

FLUXNET15, the latest update of the longest global record of ecosystem carbon, water, and energy fluxes, features improved data quality, new data products, and more open data sharing policies.


2. As Winters Get Warmer, Sugar Maples May Absorb Less Silicon

Rising temperatures that reduce snow cover leave soils vulnerable to frost, reducing silicon uptake by trees, with potential effects on downstream ecosystems.


3. How Arctic Ice Affects Gas Exchange Between Air and Sea

Scientists begin to fill a major data gap by investigating carbon dioxide dynamics in a remote region of the Arctic Ocean.


4. Better Estimates of Clouds’ Climate Effects Are on the Horizon

A recent update to an algorithm for processing satellite data could improve understanding of the variable climate effects of clouds composed of different amounts of ice and liquid.


5. Could Subsea Methane Hydrates Be a Warming "Tipping Point"?

The authors of a recent paper in Reviews of Geophysics answer questions about the potential for subsea methane hydrates to contribute to global warming.


V. Space & Planets

1. Hydrogen Molecules Hint at Habitability of Enceladus's Ocean

Scientists suggest that the hydrogen could be evidence of hydrothermal activity on the ocean floor of Saturn's sixth largest moon.


VI. Geophysical Research Letters

1. The post-2002 global surface warming slowdown caused by the subtropical Southern Ocean heating acceleration

The warming rate of global mean surface temperature slowed down during 1998–2012. Previous studies pointed out role of increasing ocean heat uptake during this global warming slowdown, but its mechanism remains under discussion. Our numerical simulations, in which wind stress anomaly in the equatorial Pacific is imposed from reanalysis data, suggest that subsurface warming in the equatorial Pacific took place during initial phase of the global warming slowdown (1998–2002), as previously reported. It is newly clarified that the Ekman transport from tropics to subtropics is enhanced during the later phase of the slowdown (after 2002) and enhanced subtropical Ekman downwelling causes accelerated heat storage below depth of 700?m in the subtropical Southern Ocean, leading to the post-2002 global warming slowdown. Observational data of ocean temperature also support this scenario. This study provides clear evidence that deeper parts of the Southern Ocean play a critical role in the post-2002 warming slowdown.


2. Arctic sea ice decline and continental cold anomalies: Upstream and downstream effects of Greenland blocking

The influence of Greenland blocking on continental cold anomalies in the Northern Hemisphere is examined. It is found that westward moving Greenland blocking (WGB) events in the recent decade are more strongly related to the sea ice decline over the Baffin Bay, Davis Strait, and Labrador Sea (BDL), while the quasi-stationary Greenland blocking (QGB) events are more strongly related to the negative phase of the North Atlantic Oscillation. The frequency of WGB events is significantly increased owing to reduced mid-high-latitude westerly winds in the North Atlantic and its upstream region because of intensified Arctic warming related to the large BDL sea ice decline. It is further revealed that North American low temperatures are more sensitive to the WGB, while European low temperatures are more sensitive to the QGB. For the WGB, an intense cold anomaly is seen over the eastern North America. But for the QGB, strong cold anomalies appear over the North Europe and eastern Asia. Thus, it is concluded that more winter cold air outbreaks should occur over the eastern North America, if large BDL sea ice decline continues in the recent decade.


3. Predicting Sargassum blooms in the Caribbean Sea from MODIS observations

Recurrent and significant Sargassum beaching events in the Caribbean Sea (CS) have caused serious environmental and economic problems, calling for a long-term prediction capacity of Sargassum blooms. Here we present predictions based on a hindcast of 2000–2016 observations from Moderate Resolution Imaging Spectroradiometer (MODIS), which showed Sargassum abundance in the CS and the Central West Atlantic (CWA), as well as connectivity between the two regions with time lags. This information was used to derive bloom and nonbloom probability matrices for each 1° square in the CS for the months of May–August, predicted from bloom conditions in a hotspot region in the CWA in February. A suite of standard statistical measures were used to gauge the prediction accuracy, among which the user's accuracy and kappa statistics showed high fidelity of the probability maps in predicting both blooms and nonblooms in the eastern CS with several months of lead time, with overall accuracy often exceeding 80%. The bloom probability maps from this hindcast analysis will provide early warnings to better study Sargassumblooms and prepare for beaching events near the study region. This approach may also be extendable to many other regions around the world that face similar challenges and opportunities of macroalgal blooms and beaching events.


4. Regional influences on reconstructed global mean sea level

Reconstructions of global mean sea level (GMSL) based on tide gauge measurements tend to exhibit common multidecadal rate fluctuations over the twentieth century. GMSL rate changes may result from physical drivers, such as changes in radiative forcing or land water storage. Alternatively, these fluctuations may represent artifacts due to sampling limitations inherent in the historical tide gauge network. In particular, a high percentage of tide gauges used in reconstructions, especially prior to the 1950s, are from Europe and North America in the North Atlantic region. Here a GMSL reconstruction based on the reduced space optimal interpolation algorithm is deconstructed, with the contributions of individual tide gauge stations quantified and assessed regionally. It is demonstrated that the North Atlantic region has a disproportionate influence on reconstructed GMSL rate fluctuations prior to the 1950s, notably accounting for a rate minimum in the 1920s and contributing to a rate maximum in the 1950s. North Atlantic coastal sea level fluctuations related to wind-driven ocean volume redistribution likely contribute to these estimated GMSL rate inflections. The findings support previous claims that multidecadal rate changes in GMSL reconstructions are likely related to the geographic distribution of tide gauge stations within a sparse global network.


5. Satellite-observed drop of Arctic sea ice growth in winter 2015–2016

An anomalous warm winter 2015–2016 lead to the lowest winter ice extent and highlights the sensitivity of the Arctic sea ice. Here we use the 6 year record of an improved sea ice thickness product retrieved from data fusion of CryoSat-2 radar altimetry and Soil Moisture and Ocean Salinity radiometry measurements to examine the impact of recent temperature trend on the Arctic ice mass balance. Between November 2015 and March 2016, we find a consistent drop of cumulative freezing degree days across the Arctic, with a negative peak anomaly of about 1000 degree days in the Barents Sea, coinciding with an Arctic-wide average thinning of 10 cm in March with respect to the 6 year average. In particular, the loss of ice volume is associated with a significant decline of March first-year ice volume by 13%. This reveals that due to the loss of multiyear ice during previous years, the Arctic ice cover becomes more sensitive to climate anomalies.


6. A reconstructed South Atlantic Meridional Overturning Circulation time series since 1870

This study reconstructs a century-long South Atlantic Meridional Overturning Circulation (SAMOC) index. The reconstruction is possible due to its covariability with sea surface temperature (SST). A singular value decomposition (SVD) method is applied to the correlation matrix of SST and SAMOC. The SVD is performed on the trained period (1993 to present) for which Expendable Bathythermographs and satellite altimetry observations are available. The joint modes obtained are used in the reconstruction of a monthly SAMOC time series from 1870 to present. The reconstructed index is highly correlated to the observational based SAMOC time series during the trained period and provides a long historical estimate. It is shown that the Interdecadal Pacific Oscillation (IPO) is the leading mode of SAMOC-SST covariability, explaining ~85% with the Atlantic Ni?o accounting for less than 10%. The reconstruction shows that SAMOC has recently shifted to an anomalous positive period, consistent with a recent positive shift of the IPO.


7. Weakening and shift of the Arctic stratospheric polar vortex: Internal variability or forced response?

Recent studies have proposed that the Arctic stratospheric polar vortex has weakened and shifted away from the North Pole during the past three decades. Some of these studies suggest that this trend has been driven by a decline in Arctic sea ice leading to enhanced zonal wave number 1 waves propagating into the stratosphere and that it has in turn contributed to a recent wintertime surface cooling over North America and some parts of Eurasia. Here trends in several measures of the location and strength of the stratospheric polar vortex from 1980 to 2016 are examined in two reanalysis products. All measures show weakening and equatorward shift trends, but only one measure, the vortex centroid latitude, has a trend which is statistically significant at the 95% level in both reanalyses. By comparing large ensembles of historical simulations with preindustrial control simulations for two coupled climate models, the ensemble mean response of the vortex is found to be small relative to internal variability. There is also no relationship between sea ice decline and trends in either vortex location or strength. Despite this, individual ensemble members are found to have vortex trends similar to those observed, indicating that these trends may be primarily a result of natural internally generated climate variability.


VII. AGU Blogs

1. Why can we see and hear meteors at the same time?

Light travels nearly a million times faster than sound. But for thousands of years, humans have reported hearing some meteors as they pass overhead, puzzling scientists for decades. Now, a new study puts forth a simple explanation for the phenomenon.


2. Researchers unravel drivers of large iceberg movement

Researchers have succeeded in modeling how Antarctic icebergs drift through the Southern Ocean, and in identifying the physical factors behind their movement and their melting. Which factors are most important tends to depend on the size of the iceberg in question



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